Automatic volume control circuit



Sept. 21, 1937.

H. E. HOLLMANN AUTOMATIC VOLUME CONTROL CIRCUIT Filed March so, 1934;

70 A/[XT 672165 INV ENTOR HANS ERICZIOLLMANN BY 7W5.

' ATTORNEY Patented Sept. 2 1, 1937 PATENT. mam

AI JTOMATI C VOLUME CONTROL CIRCUIT Hans Erich Hollmanm Berlin, Germany, assignor to Telefunken Gesellschaft fiir Drahtlose Telegraphic m. b. H., Berlin, Germany, a corporation of Germany Application March so, 1934, Serial No. r i In Germany June 29, 1933 2, Claims. (01250-20) The present invention relates to means, and a novel method, forhutomatically regulating the gain of a receiver.

Ellie invention" disclosed in application Serial No. 714,650, filed March 8, 1934, in the name of Hans Erich I-Iollmann is concerned with anelectron tube connected in what has been cal-led in recent art a brake-field circuit scheme (Barkhausen-Kurz principle), the biasing voltage of whose brake-field electrode is automatically adjusted to a statically predetermined value. According to the invention, this is accomplished by that the brake-field electrode is charged up by way of a high-ohm resistor, the brake-field circuit (briefly called the brake or retarding field circuit) being short-circuited for audio potentials by the aid of a condenser.

In the drawing, Fig. 1 shows a graphical analysis of the invention; Fig. 2 is a circuit diagram of one embodiment of the invention.

If, then, radio oscillations fall upon the retarding-field electrode, they will be rectified by virtue of the curvature prevailing in the characteristic curve at or about the working point A, and this results in an additional brake-field electrode current dib being a function of the amplitude of the radio potentials. Plotting the characteristic graph for the retarding-field scheme ib=f(eb), where lb, 61) are the current and voltage, respectively, of the retarding-field electrode, while at the same time difierent radio potentials are applied to the retardingfield electrode, then a family of graphs of the kind illustrated in Fig. 1 is obtained in which the purely static characteristic is turned, that is to say, to a measure corresponding to the impressed alternating potential.

Now, intersecting this family of curves is the straight resistance line the points of intersection between the latter and the various curves being indicated at A, A, A", etc. This representation clearly demonstrates that the working point A is caused to shift upon the arrival of radio" oscillations in that the bridging condenser is charged up. The amount of change deb of the retarding-field potential may be chosen at will by the convenient choice of the Now, according to this invention, the said :voltage variations deb fed to a tube connected in a Barkhausen-Kurz (retarding-field) circuit time as a grid'biasing voltage .for one, or more,

radio stages connected belowtheqaudion connected in a retarding-field circuitscheme, said radio stages most suitably being equipped with What is known as exponential, or variable mu, tubes.

One instance of a practical embodiment of the basic idea of this invention is illustrated in the diagram of Fig. 2. In the same the signal potentials are fed from the receiving antenna A tothe grid of the exponential, or variable mu, tube I where they are amplified and then transferred by means of the radio transformer T to the retarding-field electrode of the retarding-field audion 2. According to the aforesaid patent application, the same is connected by way of a resistance W with the positive grid potential Eg.

The audio short-circuit of the retarding-field circuit is insured by means of the capacity C, the resistance of the secondary transformer coil S2 may be disregarded so far as the modulation frequency is concerned. The fluctuations of the brake-electrode potential occurring across the condenser C then serve for the control of the grid potential of the radio amplifier tube 1 in that the grid biasing voltage Egl is tapped directly across the resistance W, or part thereof. An auxiliary voltage Bg may be used to adjust correctly the Working point of the tube 1. The higher the radio voltage arising at the retardingfield electrode of tube 2, the more markedly will be charged up the condenser C according to Fig. 1, and the higher will be the negative biasing voltage .of the exponential tube I.

This, on the other hand, will cause a reduction in gain so that the amplitude active at the retarding-field electrode will be diminished. What can be seen therefrom is that the arrangement has an equalizing effect so that, in the presence of suitable adjustment of the working voltages, fluctuations of the input amplitude of the kind occasioned by fading as well known will be thus compensated.

In the arrangement hereinbefore described compensation will be effected in the proper sense only when the retarding-field audion operates at the lower knee of its characteristic. If the working point is shifted in the upper knee region,

then the retarding field electrode, upon radio energy falling in, will be charged positive, and the gain of the exponential tube l is raised instead of being reduced.

This novel arrangement distinguishes itself by great simplicity of construction and arrangement, the threshold value of which can be considerably reduced by the provision of regeneration. It will be understood that all retardingfield circuit schemes disclosed in the aforesaid i patent application and in other places may be combined for fading compensation in accordance with the basic idea as hereinbefore disclosed, with an exponential-tube stage in that the retardingfield potential furnishes the grid voltage for the amplifier tubes.

What is claimed is:

1. In combination, in a radio receiver, a radio frequency signal amplifier tube having at least a control grid, cathode and anode and having an input circuit, a rectifier tube following the amplifier and including a cathode, anode and control grid, a tuned circuit connected between the anode and cathode of the amplifier, a source of anode voltage in circuit with said tuned circuit, a path connected between the anode and grid of the rectifier including a signal input circuit, coupled to said tuned circuit, in series with an impedance, means establishing the rectifier cathode at the amplifier cathode potential, a connection between the junction of said rectifier and said impedance and said voltage source, a condenser between the rectifier cathode and the junction of the impedance and the rectifier input circuit, and a biasing connection between the amplifier control grid and the last named junction.

2-. In a receiver including an amplifier tube of the variable mu type and a demodulator tube arranged in cascade, each tube including a cathode,

anode and control grid, a source of direct current voltage disposed in'the space current path of the amplifier, a tuned network coupling the anodes of said amplifier and demodulator, a path between the anode and grid of the demodulator including a resistor, a direct current connection between the grid side of said resistor and the amplifier anode side of said voltage source, a signal input circuit for said amplifier having one side connected to the amplifier grid, a condenser connecting the demodulator cathode to the anode side of said resistor, means establishing said amplifier and demodulator cathodes at a fixed direct current potential, and a connection between the low alternating potential side of the amplifier input circuit and the anode side of said resistor to impress on the amplifier grid a gain control bias.

HANS ERICH HOLLMANN. 

